“Mr. Trump reached out to President Clinton a few times. President Clinton returned his call in late May,” an employee for Bill Clinton told the Post. “While we don’t make it a practice to discuss the president’s private conversations, we can tell you that the presidential race was not discussed.”

A spokeswoman for Trump's campaign declined to comment for the Post report, and Hillary Clinton's campaign did not immediately offer a statement for it.

Some Republicans have voiced frustration with Trump entering the GOP race, noting his previous associations with the Clintons and donations to the Clinton Foundation, which have come under fire.

He has also admitted that he identifies with Democrats on some issues, including around the time of the financial crises, which he has used amid arguments that the country doesn't need "another Bush."

Trump is currently atop several polls, leading all Republicans presidential candidates, including former Florida Gov. Jeb Bush, by double digits heading into Thursday night's first GOP debate.

For his part, Trump has in recent weeks repeatedly labeled Hillary Clinton as the "worst" secretary of State.